What is a Casio module number and where do I find it?
The module number is the ID of the electronic movement inside your Casio — and for anything practical (manuals, parts, resets, identification), it matters more than the model name on the dial.
Where it is: stamped on the case back, inside a small rectangle or oval, usually 3-4 digits. On a watch marked "A158W" you'll find the module 593 in that box. That's the number you want.
Why it beats the model name: Casio reuses one module across many models, and sells one model with different modules across generations. Two watches that look identical can behave differently — different alarm behavior, different button sequences — because the module inside changed. When you search "how to set" anything, search the module, not the model.
What the module number unlocks:
Manuals: Casio's official support archive is organized by module. Type the module number into their manual search and the exact instruction sheet appears — for watches from decades ago, this archive is remarkably complete. See How do I find the manual for a vintage digital watch? for the full workflow.
Identification: buying vintage online, the module in the case back photo confirms what you're actually getting. A correct dial with a wrong module means a franken-watch or a swapped movement.
Parts and repair threads: collector forums index repair knowledge by module. The fix for your dead backlight was probably documented years ago — under the module number.
A note on dating: the module tells you the design generation, not the production year of your specific watch. For age, you'll combine the module with other clues — that's its own guide.
Our database lists the module number for every model we cover, right under the model name — it's the second thing we record, after the battery.
Your collection deserves better than a spreadsheet.
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